There have been a number of processes for removal of chromium from cobalt.
One process involves spray drying cobalt chloride solutions in concentrated hydrochloric acid in a ceramic dryer spray. This described in a paper entitled, "Chemical Processes for the Working up of Nickel and Cobalt Raw Materials" by A. Van Petegheim, H. Willekens, and B. Tougarinoff in Metallurgie--Hoboken.
Another method is to roast or fuse cobalt containing material with sodium carbonate forming the water soluble sodium chromate.
Still another method involves a two step precipitation of chromium from a very dilute cobalt solution. This is described in a paper entitled, "Recovery of Cobalt from Metallurgical Wastes", by D. Pearson, Warren Spring Lab--United Kingdom.
There are numerous solvent extraction methods. Bureau of Mines Report No. R17316 entitled "Chemical Reclaiming of Superalloy Scrap" by P. T. Brooks, G. M. Potter, and D. A. Martin, describes a process for recovering nickel, cobalt, molybdenum, and chromium from superalloy grindings. The process involves dissolving the metals in hot chlorinated acidic liquor, carbon absorption, solvent extraction separations, and chemical precipitations.
Some of the above named methods involve special equipment. A process in which chromium is efficiently removed from cobalt without special equipment would be desirable.